Inorganic composition for high temperature use and method of forming a millboard therefrom

Abstract

An inorganic composition useful as material for Lehr rolls at temperatures above 500 DEG C consists essentially of 15-45% chrysotile asbestos, 40-75% talc component and 2-35% inorganic binder. The composition is also used in manufacturing millboard by forming a water slurry of said composition and transferring said slurry to a rotating screen cylinder, then to a moving belt and then to a rotating drum upon which layers of said slurry accumulate upon each other and are thereafter slit, dried and formed into a flat sheet.

What we claim is: 
     
       1. A composition useful at temperatures in excess of 500°C which consists essentially of, in percentage by weight of the composition: 15-45% chrysotile asbestos fiber, 40-75% talc component, and 2-35% inorganic binder. 
     
     
       2. The composition of claim 1 wherein said talc component comprises finely divided particles of -400 mesh in size. 
     
     
       3. The composition of claim 2 wherein essentially all of said particles are of a size less than 30 microns. 
     
     
       4. The composition of claim 3 wherein the average particle size is in the range of 2-10 microns and the maximum particle size is approximately 20 microns. 
     
     
       5. The composition of claim 1 wherein said talc component comprises a major portion by weight of platey talc and a minor portion by weight of associated minerals. 
     
     
       6. The composition of claim 5 wherein said talc component comprises 60-100% by weight of plately talc and 0-40% by weight of associated minerals. 
     
     
       7. The composition of claim 6 wherein said talc component comprises 70-100% by weight of plately talc and 0-30% by weight of associated minerals. 
     
     
       8. The composition of claim 1 wherein said inorganic binder comprises hydraulic cement and montmorillonite clay. 
     
     
       9. The composition of claim 8 wherein said cement and clay are present in a weight ratio of approximately 2:1 respectively. 
     
     
       10. The composition of claim 8 wherein said cement is present as 1-20% by weight of the composition and said clay is present as 1-15% by weight of the composition. 
     
     
       11. The composition of claim 1 wherein said chrysotile asbestos comprises a mixture of approximately equal weights of grade 5 and grade 6 fibers. 
     
     
       12. The composition of claim 1 consisting essentially of, in percentage by weight of the composition: 20-40% chrysotile asbestos fiber, 45-65% talc component, and 8-27% inorganic binder. 
     
     
       13. The composition of claim 12 wherein said talc component comprises finely divided particles of -400 mesh in size. 
     
     
       14. The composition of claim 13 wherein essentially all of said particles are of a size less than 30 microns. 
     
     
       15. The composition of claim 14 wherein the average particle size is in the range of 2-10 microns and the maximum particle size is approximately 20 microns. 
     
     
       16. The composition of claim 12 wherein said talc component comprises a major portion by weight of platey talc and a minor portion by weight of associated minerals. 
     
     
       17. The composition of claim 16 wherein said talc component comprises 60-100% by weight of platey talc and 0-40% by weight of associated minerals. 
     
     
       18. The composition of claim 17 wherein said talc component comprises 70-100% by weight of platey talc and 0-30% by weight of associated minerals. 
     
     
       19. The composition of claim 12 wherein said inorganic binder comprises hydraulic cement and montmorillonite clay. 
     
     
       20. The composition of claim 19 wherein said cement and clay are present in a weight ratio of approximately 2:1 respectively. 
     
     
       21. The composition of claim 19 wherein said cement is present as 5-15% by weight of the composition and said clay is present as 3-12% by weight of the composition. 
     
     
       22. The composition of claim 12 wherein said chrysotile asbestos comprises a mixture of approximately equal weights of grade 5 and grade 6 fibers. 
     
     
       23. A method of manufacture of a millboard comprising the composition of claim 1, which method comprises forming a water slurry of chrysotile asbestos fibers, talc component and inorganic binder, transferring said slurry to a rotating screen cylinder, transferring material from said cylinder to a moving belt, and thereafter to a rotating drum whereupon a thickness is accumulated by building up layer upon layer, thereafter slitting said accumulated layers longitudinally of the drum, forming the slit layers into flat sheet form and drying said layers. 
     
     
       24. The method of claim 23 wherein said water slurry also comprises a wetting agent in an amount equal to about 0.01 to 1.0 weight % of the solids content of the composition. 
     
     
       25. A Lehr roll disc comprising the composition of claim 1. 
     
     
       26. A Lehr roll disc comprising the composition of claim 12.